As a technique in such a field, Japanese Translated PCT Application Laid-Open No. HEI 9-507326 has conventionally been known. The apparatus disclosed in this publication irradiates a bill with an ultraviolet ray, measures the level of ultraviolet light reflected by the bill with a first photocell and the amount of fluorescence generated by the bill with a second photocell at the same time, and compares the respective measured amounts with reference levels, so as to determine whether the bill is authentic or not.
However, the following problem exists in the above-mentioned conventional apparatus. Namely, while the light can be received relatively well against flopping of the bill on its conveying path when the bill is obliquely irradiated with the ultraviolet ray from thereabove, an area required in the bill may not sufficiently be irradiated with the ultraviolet ray if the bill is wrinkled or bent. In this case, the generated fluorescence may fluctuate, whereby the output by receiving fluorescence may become uneven, thus making it difficult to receive the fluorescence accurately.
In particular, it is an object of the present invention to provide a paper sheet fluorescence sensor which can accurately detect the fluorescence generated by paper sheets while not being easily influenced by the states of paper sheets.